Generally, silver halide emulsions are prepared through a sequence of steps where a soluble silver salt and a soluble halide are mixed in an aqueous solution of gelatin to form silver halide grains and physical ripening, desalting and chemical sensitization are then carried out.
Methods are known where adsorptive compounds such as dyes as crystalline phase-controlling agents are added during the course of grain formation to obtain a desired crystalline phase or to introduce defects intentionally into the crystalline phase during grain formation. These method are described in U.S. Pat. Nos. 2,735,766, 3,628,960, 4,183,756 and 4,225,666 and JP-A-61-205929 (the terms "JP-A" as used herein means an "unexamined published Japanese patent application").
Dyes as chemical sensitizing aids are often added during chemical sensitization to control chemical sensitization nuclei, thus improving the high-intensity reciprocity failure and controlling intrinsic desensitization. These methods are described in, for example, JP-A-58-113926, JP-A-58-113927, JP-A-58-113928, U.S. Pat. Nos. 4,439,520 and 4,435,501, Research Disclosure, Item 17643, Section III, JP-A-62-6251, JP-A-58-126525, JP-A-62-56948, JP-A-62-43644, JP-A-58-113928, JP-A-1-40938, JP-A-1-62631, JP-A-1-62632, JP-A-1-74540 and Japanese Patent Application Nos. 62-203635, 62-219982, and 62-251377.
Examples of the dyes which can be added in the above methods as chemical sensitizing aids include cyanine dyes, merocyanine dyes, complex cyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. These dyes are described, in, for example, JP-A-61-160739.
However, when dyes are used as the crystalline phase controlling agents, photographic performance is greatly deteriorated due to development restraint, residual color and intrinsic desensitization by adsorbed dyes. Further, when spectral sensitization is carried out by adsorbing sensitizing dyes in a subsequent stage, the crystalline phase controlling agents seriously interface with the adsorption of the dyes and there is difficulty in dye adsorption. When dyes are used as the chemical sensitization aids, the photographic performance is greatly deteriorated due to development restraint, residual color, and intrinsic desensitization by the adsorbed dyes as in the above case. In addition, when spectral sensitization is carried out by sensitizing dye adsorption in a subsequent step, the chemical sensitization aids seriously interfere with dye adsorption. Accordingly, development of a method wherein a part or all of the dyes added as crystalline phase controlling agents or chemical sensitization aids can be removed from the silver halide emulsions after completion of the formation of the grains or chemical sensitization is required.
Nitrogen-containing heterocyclic compounds having no spectrally sensitizing capability are adsorptive compounds which can be added during the course of grain formation as crystalline phase-controlling agents to obtain a desired crystalline phase or to introduce defects intentionally into the crystalline phase during grain formation, or can be added during chemical sensitization as chemical sensitization aids to control chemical sensitization nuclei. These nitrogen containing heterocyclic compounds having no spectrally sensitizing capability, when used to control the crystalline phase, exhibit the same adverse influences as the dyes which are added to control the crystalline phase of the grains, and when used as chemical-sensitization aids exhibit the same adverse influences as the dyes which are added as chemical-sensitization acids.
Silver halide solvents are adsorptive compounds which can be added during the course of grain formation as crystalline phase-controlling agents to obtain a desired crystalline phase or to introduce defects intentionally into the crystalline phase during grain formation, or can be added during chemical sensitization as chemical sensitization aids to control chemical sensitization nuclei. These silver halide solvents, when used to control the crystalline phase, exhibit the same adverse influences as the dyes which are added to control the crystalline phase of the grains, and when used as chemical-sensitization aids exhibit the same adverse influences as the dyes which are added as chemical-sensitization acids.